What is the cause of cyanobacteria outbreak (methods to control cyanobacteria)

"The lakes in China are seriously eutrophic, and cyanobacteria grow obviously, especially in the big rivers and lakes in the eastern coastal cities," Li said, but eutrophication still exists in more places. "There are cyanobacteria in Beijing's moats, Beihai and reservoirs, and the cyanobacteria in Beijing's moats also exceed the standard.

Chen Changjie, a researcher at the Institute of Environmental and Health-related Product Safety of China Center for Disease Control and Prevention, further pointed out: "Cyanobacteria need more nutrients.

Generally speaking, there is a lot of nitrogen and other nutrients in water, but there is little phosphorus. Once a large amount of phosphorus appears in the water, the outbreak of cyanobacteria is natural. So phosphorus is the decisive factor. "

When it comes to water eutrophication, people usually immediately associate it with industrial pollution. In fact, the environmental protection department of China has also formulated a series of policies and regulations to ensure that the contents of nitrogen and phosphorus in industrial emissions are within the range permitted by the environment.

The problem is that industrial emissions are not the only channel of nitrogen and phosphorus pollution. "Pollution is a comprehensive problem. Everyone is more concerned about industrial pollution, which is easy to find and therefore easy to control.

Agricultural pollution is not familiar to the public, but it is also very serious. There is a lot of farmland around Taihu Lake. Fertilizers and pesticides used in agricultural production either seep into groundwater through soil or directly discharge into rivers and flow into Taihu Lake.

Fertilizers and pesticides are rich in nitrogen and phosphorus, which is an important reason for the eutrophication of Taihu Lake. In addition, domestic pollution has also accelerated the eutrophication of toxins. Organic wastes discharged by local residents, such as feces, are flushed into sewers with sanitary equipment, and then discharged into rivers and lakes after certain treatment. It also contains a lot of nitrogen and phosphorus.

Li also believes that in recent years, cyanobacteria outbreaks in lakes such as Taihu Lake, Chaohu Lake and Dianchi Lake are closely related to the surge in population around lakes in recent years.

When cyanobacteria rot, they give off a bad smell. This smell includes two gases, "one is the smell of soil that smells like soil, and the other is 2- methyl isoborneol that smells like 666." As long as the concentration is very small, they can produce stench. "Liu Wenjun said.

Odor and foul smell can make people feel uncomfortable, but the study has not found any substantial harm to the human body. In the process of purification, activated carbon is generally used to adsorb these two odorous substances, but the effect is limited. At present, there is also ozone plus activated carbon adsorption method, which has good effect, but the price is higher.

Microcystins are not that simple. Although cyanobacteria can't parasitize humans or animals and cause diseases, they may produce a series of natural toxins that endanger human health.

These toxins usually exist in the cell membrane of cyanobacteria, so when cyanobacteria are alive, they are fine. When they die and rot, the cell membrane breaks and microcystins are released into the water.

Microcystins can be produced by species such as Microcystis, Anabaena and Tremella in cyanobacteria. Among more than 80 microcystins found so far, microcystin -LR is the most common and toxic one.

Shanghai Medical University has conducted experiments on the damage of microcystins to mice, and the results show that about 70% of toxins will be transported through the small intestine and liver and will gather in the liver, thus causing organ damage.

Chen Changjie pointed out: "Animal experiments show that microcystins may cause cancer in mice, but the impact of this situation on human body is still unclear." Some researchers also believe that this damage may not be directly caused by microcystins, but by other organic substances contained in polluted water.

For safety reasons, the World Health Organization regards microcystin -LR as one of the criteria for judging the quality of drinking water. 1 July, the country promulgated a new drinking water standard, referring to the relevant standards of the World Health Organization: the content of microcystin -LR in each liter of water should not exceed1microgram.

It is alarming that even the drinking fountains we usually use will produce cyanobacteria. Liu Wenjun said that if there is too much organic matter in the filter of the drinking machine, cyanobacteria may accumulate, so it should be replaced every six months. He also believes that it is difficult to say its harm before the new drinking water standard is formulated.

However, there is no need for the public to panic about microcystins. Even if the concentration of microcystins in water source is high, follow-up water treatment and other measures can be taken to ensure that the content of microcystins in tap water meets the new national standard. As for some aquatic products with high content of microcystins, only long-term consumption in large quantities may cause potential health hazards.

Microcystins can be produced by species such as Microcystis, Anabaena and Tremella in cyanobacteria. Among more than 80 microcystins that have been identified, microcystin -LR is the most common one. The new drinking water standard stipulates that the content in each liter of water should not exceed 1 microgram.

Once the cyanobacteria break out, salvage is the first step of emergency treatment. Therefore, we often see such a scene recently: water as thick as paint is scooped out of rivers and lakes by a spoonful.

"Salvaging cyanobacteria floating on the water surface is only an emergency measure, which can only produce the effect of being out of sight. Most cyanobacteria exist in water and sediment and cannot be salvaged. " Li said to him. This method of mechanical algae fishing is mainly used in local areas where cyanobacteria break out.

Another emergency method is "physical absorption". Adding clay to water can make cyanobacteria adsorb on clay particles and make them sink to the bottom of the water. "But this can't cure the symptoms, because cyanobacteria still live underwater and won't die. It will continue to erupt. "

The methods of killing cyanobacteria are more advanced, such as crushing cyanobacteria cells with ultrasonic waves, killing cyanobacteria cells with radiation, or affecting the activity of cells with electric fields.

"There are also methods of sinking cyanobacteria by electromagnetic waves and ultrasonic waves abroad, but even this will cause secondary pollution, because cyanobacteria are still alive and dead cyanobacteria will release toxins."

Chemical methods can also be used to remove cyanobacteria. For example, put algaecide or flocculant into water. However, these chemicals may pollute lakes, so there are high requirements for chemicals: high efficiency, low toxicity or non-toxicity, no pollution, no corrosion, low cost, safe production and transportation, and convenient administration.

Among the qualified chemicals, copper sulfate can kill cyanobacteria, and alum and lime can make cyanobacteria sink.

Because the cells of cyanobacteria are broken after being killed, microcystins are released, so chemicals with toxin adsorption function must be used at the same time. Some smaller lakes can replace the mud bottom containing cyanobacteria by changing the lake bottom to prevent the release of microcystins.

Compared with the elimination of cyanobacteria, it is more difficult to restore the damage caused by cyanobacteria to the surrounding ecology. Therefore, ecological restoration has become the focus of cyanobacteria control research. "In ecological restoration, aquatic plants can be planted to absorb nutrients in water and compete with cyanobacteria."

Li said: "But there are also some problems. When planting aquatic plants, aquatic plants will soon die, because the water body where cyanobacteria breed is very opaque or even completely opaque. Because photosynthesis cannot be carried out, it is difficult for aquatic plants to grow. "

Some experts also envisage the elimination of cyanobacteria through traditional fish farming. For example, increase filter-feeding fish and zooplankton that eat algae, such as silver carp. But this method also has limitations.

If there are few fish, it will be difficult to eliminate large areas of cyanobacteria, but if the density of fish is too high, it will also lead to new pollution. In addition, it is not easy for fish to compete with cyanobacteria.

"Due to the outbreak of cyanobacteria, the oxygen content in water will decrease due to the increase of organic matter, and fish will die of hypoxia, so you can't raise too much." Kong Fanxiang said that fish, as a link in the food chain, may also spread algae toxins in the food chain to humans.

The more advanced ecological control method is to directly attack cyanobacteria cells through microorganisms, which is very effective, but the disadvantage is that it is expensive.

Some people say that cyanobacteria are "ecological cancer", while others say that cyanobacteria are "green psoriasis", which is difficult to remove once infected. "First cut off the pollution source, and then restore the water source of the lake, including ecological restoration and physical restoration."

Liu Wenjun said, "The most fundamental way is to control pollution sources, change the mode of economic growth and change the mode of industrial structure." It is more important to strengthen environmental early warning and eliminate cyanobacteria outbreaks before they occur.

Some people say that cyanobacteria are "green psoriasis", and once infected, it is difficult to remove them. First, cut off the pollution source, and then restore the water source of the lake, including ecological restoration and physical restoration. The most thorough way is to control pollution sources, change the mode of economic growth and change the mode of industrial structure.